As we enter the multimedia age, due to demands to increase the capacity and speed of data processing in optical communication systems and computers, transmission systems using optical transmission mediums have come to be used in public telecommunication networks, LANs (i.e. local area networks), FAs (i.e. factory automations), interconnects between computers, household wirings, and the like.
Among components constituting the transmission system, an optical waveguide is a basic constituent of optical devices for realizing optical computers or high-capacity communications such as movies, moving images, and the like; optoelectronic integrated circuits (OEIC); optical integrated circuits (Optical IC); and the like. Since there is a very large market for the optical waveguide, diligent study on the optical waveguide has been conducted, and especially, a product with higher performance and lower cost is needed.
Conventionally, silica optical waveguides and polymer optical waveguides have been known as the optical waveguide.
Of these, silica optical waveguides have the advantage of having low transmission loss, but many steps such as a vitrification step at high temperature (at least 120 degree C.) and an etching process are required, resulting in a difficulty in improving manufacturing efficiency.
On the other hand, polymer optical waveguides seem to be promising in the future since the polymer optical waveguides have the advantages of the easiness of processing and the freedom of choice in selecting materials, and the like. Therefore, in addition to commodity materials such as poly(methyl methacrylate) and the like, there have been developed various materials having more excellent properties.
For example, there has been recently proposed a technique in which a radiation-sensitive composition containing an epoxy resin is used to manufacture an optical waveguide which has excellent aligning accuracy and the like.
Specifically, there has been proposed an optical waveguide comprising at least a core portion and a clad layer which covers the core portion and has a lower refractive index than the core portion, in which the core portion is a photo-cured product or a heat-cured product of a mixture of a monomer or a oligomer having an epoxy ring (e.g. an epoxy UV monomer having a specific chemical structure) and a polymerization initiator (see Japanese Laid-Open Patent Publication H8-271746).
This optical waveguide is especially for single-mode, and can be optically coupled with other optical components with easiness, low loss and an aligning accuracy of less than 10 micrometers.
Also, there has been proposed a material for forming an optical waveguide capable of transmitting an optical signal therein, which comprises the first compound having an oxetane ring, the second compound for initiating polymerization by chain reaction (specifically, a cationic polymerization initiator), and the third compound having an oxirane ring (for example, a glycidyl epoxy resin such as bisphenol A epoxy resin and the like), and which can be cured by an energy beam (see Japanese Laid-Open Patent Publication 2000-356720).
By using the above material for an optical waveguide, the chain reaction can proceed rapidly, and it is possible to obtain a highly cross-linked polymer having excellent solvent resistance.
Generally, epoxy resin is also used as a sealant for an optical module.
For example, there has been proposed a method for manufacturing an optical module, which comprises: a step in which a light path between several optical components such as a light emitting element etc, mounted on a base substrate is precoated by an light-transmitting resin; a step in which the light path is covered with a photocurable resin which comprises an epoxy resin having an epoxy equivalent of from 160 to 250 g/eq selected from among novolac type epoxy resins etc, an inorganic filler, and a photo-acid generator as essential components; and the like (see Japanese Laid-Open Patent Publication H9-243870).